High-frequency transformer for the transmission of electric impulses



July 14, 1953 Filed June 21, 1949 Permanent Magnet 5-Shorf-circuf Conductor [III l/vfwron HUGO GEORG BRUIJ NING ff/ff Patented July 14, 1953 UNITED STATES PATENT @OFFICE 'HIGHsFREQUENcY TRANSFORMER'FOR I'run LTRANsMlssIoN F ELEcTaic-iMrunsEs, n a 4i y Hugo Georg Bruijning, Eind-hoven,Netherlands,A a assigner to Hartford National Bank and Trust Company, Hartford, Conn., as trustee,

Application June 21, 1949, Serial No. 100,436 I In the Netherlands Llulyf14, 1948 has hitherto been made of la transformer which comprises a ferro-magnetic circuit, for example of rolled sheet iron, which is adapted to be magnetised to a comparatively high magnetic induction before exceeding thev limit which is set t0 the magnetic induction by the bend of the magnetisation curve of the magnetic material.` The disadvantage of the use of rolled sheet iron is that the losses are comparatively high, so that the material becomes more and more unsuitable for an impulse-recurrence frequency of more than several kc./s. In this respect it has been found that ferrite, which is highly permeable and substantially non-conductive, yields better results, notably the ferrite as described in prior Patent application Serial No. 78,432, led February 25, 1949, which ferrite is likewise magnetisable to a very high induction. The ferrite described in this application consists of a manganese ferrous-ferrite having the formula MO-FezOa, where M represents bivalent iron and manganese, in which iron and manganese atoms are in the ratio between 4.0:1 and l.5:l, and the ferrite has a Curie point exceeding 250 C.

The present invention has for its object to prop vide a method by which the maximum permissible magnetic induction can apparently be further increased, which permits a larger primary impulse to be transmitted in an undistorted manner. In other words the transformer is suitable for a higher power. According to the invention, a constant magnetic iield is produced in the magnetic circuit by means of a permanent magnet, due to which liield, in the absence of an impulse, the ferro-magnetic material of the circuit tends to become saturated, the magnetic iield produced by the pulses opposing the said constant magnetic eld, a closed conductor consisting of electrically conductive material being provided between the permanent magnet and the magnetic circuit.

In order that the invention may be more 2 claims. (01..,317-9210) similar secondary pulses of, say kilovo'lts, use

n a i2" clearly understood Vand readily carried into effect it will now -be describedmore fully with reference totheYaccornpanying-diagrammatic drawing, given by wayofexample, in which Fig. 1 represents one embodiment-thereof, Fig. 2 being a Ygraph (magnetisation curve) showing the magnetic inductionBas a function of the magnetic iield strength H of lthe material in the magnetic circuit'. f

Fig. l represents a high-frequency transformer for the transmission of electric impulses in an undisto-rted manner, sltl comprises a ferro-magnetic circuiti carrying a primary winding 2 `andfa secondary winding V3. For the sake of -ec-learness thesefwindingswhich actually are arranged Vas ,close-i-ogetlF-ier aspossible, are spatially separated .in the!drawing.v A primary voltage impulse ,of-sayfl- O kilovolts is supplied to the primary winding `2 and an ampliiied but undistorted voltage impulse of, say, 200 to 500 kilovolts is required to be taken from the secondary winding 3. To this end, it is necessary that the magnetic circuit I should not involve excessive distortion of the voltage impulse fed to the Winding 2, and that the size of the magnetic circuit and the windings should be as small as possible, in order to reduce the leakage inductances and the parasitic capacities of the two windings as much as possible. As appears from the magnetisation curve shown in Fig. 2, the magnetic inductance B of the ferro-magnetic material of circuit I can be permitted to vary only between a value Zero and a given maximum inductance Bm, where the magnetisation curve tends to depart materially from linearity. Thus, a limit is set to the size of the primary impulses, which limit is determined by the maximum primary iield strength Hm associated with this maximum inductance.

When, however, a constant magnetic eld is made operative in the magnetic circuit, the magnetisation produced by the primary impulses is not restricted to the range from 0 to the maximum Value Bm, but it may vary from a value -Bm to -i-Bm, provided that the constant magnetic eld operative in the magnetic circuit is such that, in the absence of a voltage impulse, the magnetic circuit tends to become saturated to a value -Bm.

The constant magnetic field might, for instance, be produced by means of a separate winding on the magnetic circuit, which winding is traversed by direct current. If this direct current winding is provided in the immediate Vicinity of the primary and secondary windings 2 and 3, it is necessary, in order to avoid a highfrequency short-circuit by this winding, to insert a high-frequency choke in the electric circuit the said auxiliary winding, whereby the circuit-arrangement is made expensive. Alternatively, the auxiliary winding may be provided on the magnetic circuit so as to be spaced from the primary and secondary windings 2 and 3. In this event, the short-circuit then constituted by this winding in regard to high-frequency currents only brings about that the magnetic eld produced by the pulses is locally suppressed in the ferro-magnetic material. However, an additional auxiliary winding involves the drawback that the magnetic circuit has an undue size. Moreover, this auxiliary winding absorbs energy.

The embodiment shown in Fig. 1 comprises a permanent magnet 4 which produces a magnetic induction -Bm in the absence of impulses in the ferro-inagnetic material of circuit I. In order to prevent the high-frequency magnetic eld produced by the impulses from suffering excessive losses in the material of the permanent magnet t, a. closed conductor, for example a plate 5 of electrically conducting material, is provided between the permanent magnet 4 and the remainder or the magnetic circuit l. Due to this, Foucault currents are induced in the said conductor, and the high-frequency field in the magnetic circuit l is locally suppressed, but otherwise losses are not caused.

What I claim is:

1. A pulse transformer comprising a closed magnetic circuit comprising a ferro-magnetic ferrite core portion and a permanent magnet portion producing in said core portion a constant magnetic iield having an intensity at which the core portion tends to become saturated, primary and secondary windings Wound on said core portion, and a short-circuit electrical conductor disposed between the entire core portion of the magnetic circuit and the entire permanent magnet portion, whereby when pulses of current are flowing through said windings in a direction producing a eld in said core portion in opposition to the eld produced therein by the permanent magnet substantially distortionless transformation of the pulses is obtained.

2. A pulse transformer comprising a ferromagnetic ferrite core constituted by a generally U-shaped member, a permanent magnet constituted by a bar-shaped link ixedly connected across the ends of the U, primary and secondary windings wound on said U-shaped member, said permanent magnet inducing in said core a constant magnetic iield having an intensity at which the core tends to become saturated, and an electrically conductive sheet disposed between the entire bar-shaped link and the ends of the U, whereby when pulses of current are flowing through said windings in a direction producing a eld in said core in opposition to the field produced therein by the permanent magnet substantially distortionless transformation of the pulses is obtained.

HUGO GEORG BRUIJNING.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 378,320 Kennedy Feb. 21, 1888 743,444 Burgess Nov. l0, 1903 2,040,768 Edwards May 12, 1936 2,096,801 Grant Oct. 26, 1937 2,395,881 Klemperer Mar. 5, 1946 

